Bacterial endotoxic lipopolysaccharides (LPS) are well recognized for their almost ubiquitous capacity to stimulate mammalian host inflammatory and mediator cells. Prominent among those cells which are activated by LPS is the macrophage. Responses of the macrophage to LPS include: increased synthesis and secretion of cytokines (IL-1, TNF, IL-6, IFNalpha/beta), modulation of membrane receptors and other surface antigens, and importantly, activation for tumor cell killing. The broad long term objective of the research to be undertaken in this project is the delineation of the initial biochemical interactions between various LPS preparations and mouse macrophages which lead to macrophage activation for cytokine gene expression and tumor cell cytotoxicity. The overall structure of the LPS macromolecule is well understood and it is now generally recognized that eh isolated, chemically conserved lipid A component of LPS can function as a stimulus for monocytes and macrophages. However, the role of carbohydrate determinants in mediating the expression of LPS dependent macrophage stimulating capacity has not been defined. Experiments are outlined in the first specific aim of this proposal to investigate potential hydrophobic and/or carbohydrate-specific interactions between LPS and the macrophage membrane as important contributing factors for biochemical triggering events. The responses of macrophages to different LPS preparations will be correlated with early biochemical effects of these molecules in experiments designed to evaluate in detail these structure-function relationships. A second specific aim focuses upon the role of specific 80 kDa LPS receptor glycoproteins and possible receptor linked accessory molecules (such as G proteins) in delivering activation signals. Experiments to date in our laboratory using hamster monoclonal antibodies with specificity for this 80kDa protein have established that this macrophage membrane protein is a functional receptor for LPS; however, it is postulated that an additional LPS-triggering pathway involving KDO-specific determinants may also contribute to macrophage activation via a 38kDa receptor. An important hypothesis to be examined in close collaboration with Dr. Suzuki (Project #2) is that intact LPS and the isolated purified lipid A active component of LPS may mediate macrophage activation via fundamentally different biochemical pathways. The third specific aim proposes collaborative studies with Drs. Russell (Project #3) and Parmely (Project #4) to investigate the interrelationships between LPS receptor expression on macrophages and expression of receptors for interferon and or plasminogen activator. The elucidation of the precise biochemical pathways utilized by LPS to achieve macrophage activation will have important implications for potential immunotherapeutic approaches to cancer as well as to problems of infectious disease.